Part I: This study is intended to partition left ventricular oxygen consumption between isovolumic phases of left ventricular contraction and ejection by varying independently the mechanical determinants of these phases of contraction. The data generated by this investigation will be used both to test the hypothesis that alterations in ventricular ejection have relatively little effect on myocardial oxygen consumption if the determinants of isovolumic contraction are kept constant and to develop a mechanical model which can accurately predict oxygen consumption under widely varying hemodynamic conditions. Part II: The major objective of this study is to validate the gamma camera approach to assessment of Thallium redistribution kinetics to provide a means of determining the severity of myocardial ischemic damage and its response to intervention. Part III: The purpose of this study is to define the differences, if any, between hypothermic ischemic arrest and hypothermic potassium cardioplegia in patients undergoing coronary artery bypass surgery. Part IV: The main objectives of this proposal are to examine the effects of plasma ionized calcium concentration on relaxation in the canine left ventricle and on regional transmural myocardial blood flow. Part V: The objective of this proposal is to examine left ventricular regional function by means of pulse transit sonomicrometry in the canine left ventricle under controlled hemodynamic conditions and to compare regional with global left ventricular function. Particular attention will be directed to the end-systolic pressure-chord length relationship. A subsidiary objective is to compare and validate a flexible computer program for the analysis of tape-recorded physiologic data.